The human penis is an external male intromittent organ that additionally serves as the urinal duct. The main parts are the root (radix); the body (corpus); and the epithelium of the penis including the shaft skin and the foreskin (prepuce) covering the glans penis. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The human male urethra passes through the prostate gland, where it is joined by the ejaculatory duct, and then through the penis. The urethra traverses the corpus spongiosum, and its opening, the meatus (/mi??e?t?s/), lies on the tip of the glans penis. It is a passage both for urination and ejaculation of semen. (See: male reproductive system.)
Most of the penis develops from the same tissue in the embryo as does the clitoris in females; the skin around the penis and the urethra come from the same embryonic tissue from which develops the labia minora in females.12 An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. Spontaneous non-sexual erections frequently occur during adolescence and during sleep.